1. Field of the Invention
The invention is based on a method of determining gas components and/or gas concentrations in gas mixtures, particularly in exhaust gases of internal combustion engines, in which the adsorption and/or desorption speeds of the gas mixture caused by a change in gas concentration at a gas sensor are evaluated.
2. Description of the Related Art
A generic method of determining different gas concentrations of a gas mixture in which the concentration of the gas mixture is modulated in a defined manner in a reaction chamber disposed upstream of a gas sensor is known from Sensors and Actuators, 20 (1989), 277-285. The sensor signal following the modulation is analyzed, and subsequently a conclusion is drawn regarding the corresponding gas components. This method is refined in Sensors and Actuators B, 4 (1991), 337-343 in that a sudden switch between a reference gas and the measured gas has a surging effect on the gas concentration at the gas sensor. A conclusion regarding the gas species is then drawn from the reply function of the sensor signal. In both known methods, the change in the gas mixture concentration takes place in the gas phase, because of which the influenced gas mixture only reaches the sensitive region of the gas sensor by way of a diffusion step. The system thus has a long reaction time. Moreover, the reply function is distorted by the occurring gas diffusion. Finally, the gas diffusion limits the possible frequency spectrum of modulation.
A sensor arrangement for determining CO concentrations, in which an electrochemical oxygen pump cell pumps oxygen to a gas sensor, is also known from Sensors and Actuators B, 9 (1992), 183-189 and 233-239. The gas sensor in this instance is disposed in a measuring chamber without a defined reference to the pump cell and the gas mixture. It is only required that a sufficient oxygen concentration be present at the measuring element. It was determined that the resistance value of an SnO.sub.2 gas sensor is three times greater in CO in air with 21% oxygen than in CO in nitrogen.